With the development of wireless technology and wireless applications, the demand for higher mobile data rate keeps growing rapidly. The sub 6-GHz frequency bands widely employed in wireless systems nowadays have already been crowded, and they can no longer be sufficient to meet such a challenging demand, as shown in the research paper “Millimeter Wave Mobile Communications for 5G Cellular: It Will Work!” by T. S. Rappaport et al. published in IEEE Access, vol. 1, pp. 335-349, 2013 (Rappaport et al. 2013). To overcome the global spectrum shortage challenge of the upcoming Fifth Generation (5G) wireless systems, exploiting the much broader available spectrum of centimeter and millimeter wave above 6-GHz, e.g., 28 GHz, 60 GHz, etc., has been considered as a promising solution (Rappaport et al. 2013). For the sake of simplicity, all frequency bands of centimeter, millimeter or even shorter wavelengths are all referred to as millimeter wave (mmWave) hereafter.
Although a mmWave system can provide huge bandwidth, its coverage is limited by its strong propagation directivity, large propagation loss, and high sensitivity to blockage, as shown in “Millimeter-Wave Cellular Wireless Networks: Potentials and Challenges,” by S. Rangan et al. published in Proceedings of the IEEE, vol. 102, no. 3, pp. 366-385, March 2014. For a mmWave BS, the large propagation loss is compensated by employing the antenna array that offers high array gain, while the strong propagation directivity can be overcome by employing multiple antenna arrays facing different directions where each antenna array can generate multiple radio beam patterns to cover multiple directions. However, because of the high sensitivity to blockage, multiple BSs are needed to cover an area with obstacles such as buildings, side streets, or hallways. FIG. 1 illustrates a simple example in which two mmWave Base-Stations (BSs) 1 serve two mmWave User-Equipments (UEs) 2 simultaneously in an area with one obstacle 3. In this example, both UE1 and UE2 need to be served, but only UE1 is in the Light-of-Sight (LoS) coverage area of BS1. If only BS1 is deployed, due to the large blockage loss in mmWave systems, it cannot serve UE2 blocked by the obstacle hence out of its LoS coverage area. As a result, the system coverage needs to be improved by deploying BS2 to offer LoS coverage to the area where the signal from BS1 is blocked by the obstacle. Note that each BS needs to have an optical fiber or cable connection to provide the data connection to the network, e.g., backhaul or fronthaul. Unfortunately, the need of optical fiber or cable connections to multiple BS sites increases the network deployment cost.
One alternative method to improve the system coverage is to deploy repeaters, Amplify-and-Forward (AF) or Decode-and-Forward (DF). A repeater enables a mmWave beam signal from a BS to cover an area by changing its direction, e.g., turning a corner to cover a side street or side hallway without the need to lay a fiber or cable connection to the site of the repeater. Because repeaters do not require optical fiber or cable connections, the network deployment cost can be much lower than deploying multiple BSs. However, in the case of mmWave systems, the strong signal propagation directivity also limits the coverage of a Conventional Repeater (C-R) with fixed transmitting and receiving directions. FIG. 2 illustrates a simple example in which a C-R 4 is deployed to improve the coverage for the area where the signal from the BS is blocked. In this example, similarly to FIG. 1, due to the large blockage loss in mmWave systems, BS1 cannot serve UE2 and UE3 blocked by the obstacle. Instead of deploying a second BS as in FIG. 1, a C-R with fixed transmitting and receiving directions is deployed at a location where it can receive the signal from BS1, amplify it, and forward it to part of the blocked area. Due to the strong signal propagation directivity of the mmWave signal, the C-R in this example can only provide extended LoS coverage between the two dotted lines. Since UE2 is in this extended coverage area, it can be served by the BS through the C-R. However, because UE3 is out of this extended LoS coverage area, so it still cannot be served by the BS. In summary, in a mmWave system, deploying a C-R at a location where the signal from the BS is blocked might not be able to provide sufficient coverage to that area. As a result, to cover the same blocked area that can be properly served by deploying an additional BS, tens of C-Rs might need to be deployed, which is inefficient for deployment and significantly compromises the cost advantage of deploying C-Rs.
This invention avoids the high costs of laying many fibers for high bandwidth backhauls, fronthauls or other variants to densely deployed very high throughput small cells, which are base stations or access points with small or hotspot coverage area and throughput of tens to hundreds of Gbps. Their signals are typically transmitted using wide bandwidth in high frequency bands with carrier frequency from above 3 GHz to 10's or 100's of GHz. We refer to all these high frequency bands as mmWave for convenience. For example, the carrier frequency can be 28 GHz, 70-80 GHz or above 100 GHz and the signal bandwidth can be 500 MHz or above 1 GHz. With this invention, the conventional fronthaul or backhaul or other variants are eliminated. This invention provides a method to effectively improve the coverage of a mmWave system by employing improved smart repeaters capable of scanning. A smart repeater of this invention is also referred to as a Distributed Wireless Smart Antennas (DWSA).